Evaluation. Background

Transcription

1 1 of 8 Evaluation Background This mini booster complements Mini boosters 1, 2 and 3: Accuracy and reliability, Evaluating a practical technique and What do we mean by evidence? (Science intervention materials, DfES and on this CD in Resources to show pupils about obtaining and presenting evidence, considering evidence, evaluation). Accuracy and reliability helps pupils to: consider the accuracy of measurements using different pieces of equipment; make judgements about accuracy; understand that a limited range of data can yield unreliable evidence; understand the value of repeat readings. Evaluating a practical technique helps pupils to: identify odd-looking results; consider possible practical reasons for this; suggest how to improve the practical procedure. What do we mean by evidence? helps pupils to: make sensible decisions about what evidence to collect; decide if they have a suitable range of data; decide what is relevant evidence; distinguish between fact and opinion. Additional Mini boosters 5 and 6 ( Describing patterns and Understanding variables ) should be covered before this mini booster. Describing patterns helps pupils to: identify variables and describe patterns between them; identify and interpret patterns in data; construct tables of results to show patterns; describe patterns in graphs; understand that reordering data can show patterns more easily; link patterns to their predictions. Understanding variables helps pupils to: understand about the different types of variables;

2 2 of 8 make links between the enquiry question and the independent/dependent variable; understand the importance of sensible quantities for the fixed and independent variables; select meaningful ranges and values for the independent variables; see that not every investigation is a fair test! A pupil working at: Level 4 can identify obvious anomalous results; can decide whether their enquiry was valid or not; can suggest improvements to the work, giving reasons. Level 5 can identify anomalous results and begin to explain them; can think of possible reasons why the enquiry might not be valid; makes practical suggestions about how their working methods could be improved. To move pupils from level 4 to level 5 1. Teach them about the purpose of evaluation in science. 2. Teach them about the different aspects of evaluation. 3. Scaffold their evaluations initially. Suggested teaching sequence The following activities could all be done in one lesson or split into separate activities and spread over more than one lesson. 1. To teach pupils about the purpose of evaluation in science Ask pupils to discuss what evaluation means in science, what they are expected to do and why they find it difficult. Evaluation in science should not only be considered at the end of an enquiry. Pupils should be evaluating all the way through an investigation (e.g. during the planning stage, ongoing evaluation might cause them to change the range of the independent variable, or, when obtaining evidence, they may decide that the measuring instrument they are using is not accurate enough and might pick a different one or decide to repeat more readings). When they are evaluating, pupils should be considering if the enquiry is valid by asking three questions. Can I trust my evidence?

3 3 of 8 Does my evidence support my conclusion? Have I used all the evidence? (Not just selected the bits to make my prediction right!) Use page 6, Understanding evaluation words, to check that pupils are clear about the meaning of terminology such as: fair test; reliable; accurate; error; uncertainty. The sheet will need to be cut up so that pupils can match statements to the terminology. Point out to pupils that scientific enquiry is not synonymous with a fair test. Errors in making measurements can be caused by human error (people making mistakes in reading or calibrating, or failing to zero an instrument) or because the measuring instrument is faulty or not accurate enough for the task. Pupils may be uncertain about results because they had problems reading the scale, had to estimate the reading or could not control all the variables. Some pupils go through the motions of repeating measurements three times and find the average as part of a fair test recipe, but they mix this up with keeping everything the same and miss the point of the procedure as a check on the reliability of data. Set up a circus of apparatus where individual pupils have to read the instruments and write down the results. For example: a volume of water in a measuring cylinder; a volume of water in a beaker (so pupils have to estimate the value); finding the weight of an object using three identical Newton meters (have at least one that does not give the same reading); finding the weight of an object using the same Newton meter three times; finding the temperature of a water bath using a mercury thermometer, an alcohol thermometer and a temperature probe; finding the mass of an object using a spring balance. From these results highlight the occurrence of human error. Explain that even though they have all read the same set of apparatus, there are differences and why this is. Also point out that: the same measuring apparatus can give different readings and different types of instruments can give different readings (both of which can lead to uncertainties in the results); if a measuring instrument is accurate then it measures very closely to the true reading;

4 4 of 8 if repeat readings are clustered together they are generally taken as reliable but they could be inaccurate if a faulty measuring instrument was used, so giving the same consistent wrong reading. 2. To teach pupils about the different aspects of evaluation Use other mini boosters to teach pupils about the following aspects of evaluation. Accuracy of measuring instruments (Mini booster 1) Accuracy of reading the instruments (Mini booster 1) Anomalous results and whether these results should be included, left out or repeated (Mini boosters 1, 2 and 5) Reliable results (Mini booster 1) Enough results to show a pattern (Mini booster 5) Link the pattern to the prediction (Mini booster 5) Correct variables chosen (Mini booster 6) Variables not easy to control (Mini booster 6) Range of independent variables (Mini booster 6) Sensible quantities for variables (Mini booster 6) Appropriate sample size (Mini booster 6) Was it a fair test? (Mini booster 6) Improving the practical technique (Mini booster 2) Errors and improvements (Mini boosters 1 and 2) Use the exercise on writing evaluations from Literacy in science, handouts 3.34 and 3.35 (DfES 0560/2002 and on this CD in Resources to teach pupils about evaluation), in which pupils use a guidance sheet to help them decide what a good evaluation should include. Instructions and further guidance for the task are provided on handouts 3.33 and If pupils are aware that there are different types of scientific enquiry, just revise these with them. If not, use task F (handouts 3.4 and 3.5) from the Scientific enquiry unit (DfES 0348/2002 and on this CD in Resources to teach pupils about planning) or unit 4, What kind of question, what kind of enquiry?, from AKSIS Investigations: developing understanding in scientific enquiry (available from the ASE ISBN X). Make the point that not all of the points on the checklist will apply to every type of enquiry. They are going to decide this in the next exercise. Use page 7, Evaluation checklist, and page 8, Types of enquiry to decide which evaluation statements would apply to which types of enquiry. You can give pupils a few copies of the checklist already cut up so that they only have to place them in the correct boxes, or they can write the statements in the boxes themselves, or different groups could take different enquiries.

5 5 of 8 This could be used to produce a class version that is typed up to act as a scaffold for pupils or as a large version displayed on the wall. Use units 16 20, How fair was our test?, How accurate were our measurements?, Were our results reliable?, Was our sample size large enough? and Evaluating the evidence, from AKSIS Investigations: developing understanding in scientific enquiry (available from the ASE ISBN X). 3. To help scaffold their evaluations initially As shown in the previous exercise, there is no single template that can be used for evaluating all enquiries. Pupils find the evaluation of scientific enquiries difficult and need to be encouraged to evaluate at various stages of an enquiry. Prompt sheets and writing frames can help by providing a scaffold for pupils but they should be removed once pupils are more confident. Use prompt sheets for enquiries. Be clear about what the sheet is for, for example, a writing frame; to help thinking; or questions to answer. Encourage pupils to write their own checklists based on the exercise in the section above. Use the guidance on writing evaluations from Literacy in science (DfES 0560/2002 and on this CD in Resources to teach pupils about evaluation), with examples of pupils work, to decide what could improve those evaluations. Use unit 15, Relating evidence to scientific knowledge, from AKSIS Investigations: developing understanding in scientific enquiry (available from the ASE ISBN X). Use opportunities to evaluate second-hand data when studying scientific content.

6 6 of 8 Understanding evaluation words Copy and cut up the statements in both tables. The five statements in bold (fair test, accurate, reliable, error and uncertainty) are used as headings and pupils have to discuss in groups which heading the other statements are describing. Fair test Reliable Accurate Error Uncertainty We forgot to zero the Newton meter each time Our thermometer read the same as six others in the class We did the measurements three times and then we found the average We forgot to measure the height of the plant at the start of the experiment but assumed it was about 10 cm Some people make mistakes Because humans are different we can t control all the variables It was difficult to read the scale and sometimes we just sort of estimated We kept all the variables the same except for the one we were changing When we repeated our readings they were nearly always the same We didn t line up the bottom of the meniscus with the scale My watch wakes me up at the same time every morning We used the same meter each time and the same person to read it We multiplied the mass of the object by 100 to find its weight in newtons

7 7 of 8 Evaluation checklist Have I got enough results for a pattern? Can I trust the evidence? Was my sample size big enough? Did I identify all the variables? Did I change one variable and keep the rest the same? Did I measure accurately? Did I repeat my measurements and find the average? Did I use sensible quantities for my variables? Were there any variables I couldn t control? Were there any odd results? Did I include these or leave them out? Were there any problems with the equipment? Did I have a good range for my independent variable? Did I change the independent variable by equal values to help show a pattern? Where could I have made errors? Did I pick the right independent and dependent variables to answer the enquiry question? Have I used the best way of displaying my results to show a pattern? Has all the evidence been used to decide if my prediction was correct? Has the evidence I collected raised more questions? What are they? Can I improve my investigation or enquiry? Can I say how any improvements might provide better evidence? Why?

8 8 of 8 Types of enquiry Surveys and correlations (looking for patterns) Using secondary sources (looking up information in a book or from the computer) Controlling variables (fair test) Identification and classification (grouping things or deciding which group something goes in) Using and evaluating a technique (checking why a particular thing is done, e.g. putting lime on the garden) Exploration (observing or measuring something over a long time)