University of California Press

Table 5.

Paired t-test comparisons of percentage improvement on pretests and posttests for students grouped by level of prior understanding, based on pretest scores (excludes students earning 100% on the pretest).

Groups (Pretest Percentage Earned)	One (≤50%)	Two (51–79%)	Three (80–99%)
Pretest percentage (⁠ $\bar{X}$ ± SE)	44 ± 1	65 ± 1	84 ± 1
Posttest percentage (⁠ $\bar{X}$ ± SE)	71 ± 3	80 ± 2	92 ± 1
n	51	113	108
t	7.952	9.969	8.252
p	<0.001	<0.001	<0.001
Cohen's d	1.114	0.938	0.794

Groups (Pretest Percentage Earned)	One (≤50%)	Two (51–79%)	Three (80–99%)
Pretest percentage (⁠ $\bar{X}$ ± SE)	44 ± 1	65 ± 1	84 ± 1
Posttest percentage (⁠ $\bar{X}$ ± SE)	71 ± 3	80 ± 2	92 ± 1
n	51	113	108
t	7.952	9.969	8.252
p	<0.001	<0.001	<0.001
Cohen's d	1.114	0.938	0.794

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