Jelly Crystals
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Approach:  Team
Level: Year 4 and year 8
Focus: Design a fair test experiment into the dissolving
rates of jelly crystals		  
Resources:
Jelly crystals, jug of hot water, jug of cold water,
2 plastic glasses, 2 teaspoons, recording sheet, stopwatch
336Kb
Questions/instructions:  


Preparation: Jug of hot water. Don’t hand out equipment yet.

This activity involves testing jelly crystals. In your team you will design a test
to find out if jelly crystals dissolve faster in hot or cold water. You will need to do a fair test. In a fair test, only one important thing is changed at a time
(for example, the temperature of water).

In your team think about how you will do your test. Here is some equipment you
will be able to use. When you have decided on how to do the test I will ask you
to tell me what you will do.

Hand out equipment. Allow time.
 
% responses
2007 ('03)
y4
y8
1. Tell me how you will do the test so that it is a fair test.
Record team response.
Plan:
same amount of water
29 (36)
78 (91)
same amount of jelly crystals
49 (72)
84 (98)
start timing for both as soon as water or jelly crystals are added
36 (41)
65 (59)
emphasis on treating both alike
(e.g. stir both at same speed and intensity)
24 (34)
51 (55)
careful observation and timing of when dissolving is complete
40 (44)
57 (58)
2. How will you know which one dissolves fastest?
 
compare the times it takes to dissolve all jelly crystals
42 (51)
53 (74)
3. How is your test a fair test? You explain it to me and I will write it down to
help you during your test.

Record team response.
 
not marked
•
•
You can now do your experiment. After you have done the test, you will tell me
what you found out.
Actual experiment:
used same amount of water
63 (64)
86 (96)
used same amount of jelly crystals
71 (93)
94 (94)
started timing for both as soon as jelly crystals or water added
48 (62)
75 (80)
emphasis on treating both alike (e.g. stir both at same speed and intensity)
32 (35)
63 (67)
watched carefully for dissolving to be completed/timed accordingly
75 (65)
91 (89)
compared specific times it took to dissolve
22 (31)
39 (45)
4. Do jelly crystals dissolve faster in hot or cold water?
 
hot
88 (92)
100 (100)
5. What else did you find out?

6. Now I want you to look at what you told me you would do to make sure it was a fair test.
Is that what you did?

7. Tell me about how that part went.
Retrospective evaluation:
(suggested corrections)
same amount of water
9 (13)
11 (6)
same amount of jelly crystals
3 (9)
6 (2)
start timing for both as soon as water or jelly crystals are added
8 (9)
10 (17)
emphasis on treating both alike (e.g. stir both at same speed and intensity)
9 (13)
31 (46)
careful observation and timing of when dissolving is complete
14 (4)
5 (15)
compare specific times it takes to dissolve
6 (4)
6 (6)
Participation in planning,
experiment and discussion:
all students participated
84 (70)
81 (83)
all except one student participated
13 (26)
17 (15)
half of the students participated
3 (4)
2 (2)
less than half of the students participated
0 (0)
0 (0)

Total score:
12–18
4 (10)
17 (22)
10–11
13 (7)
36 (50)
8–9
17 (30)
33 (21)
6–7
26 (33)
13 (7)
0–5
40 (20)
1 (0)
Commentary:
Because this is a team task, no graph of subgroup performance is possible. Year 8 teams generally showed much stronger understanding of fair testing requirements. At both year levels, but especially year 4, there was a marked decline in performance between 2003 and 2007.