Table 3.

Regression - Mathematics predicted.

Predictor measures	GCSE Maths Predicted			Maths Web-test Predicted
	Standardised coefficients			Standardised coefficients
	β	t	η2	β	t	η2
1st step: Perceived learning environment
Classroom Environment	0.26	11.90⁎⁎		0.23	10.47⁎⁎
	F(1,1924) = 141.61; p = 0.000; R2 = 0.07			F(1,1924) = 109.65; p = 0.000; R2 = 0.05
2nd step: Intrapersonal factors added
Classroom Environment	0.03	1.58 (♦)		0.00	-0.17
Maths Self-efficacy	0.52	22.33⁎⁎		0.50	21.41⁎⁎
Maths Interest	0.12	5.62⁎⁎		0.13	6.21⁎⁎
Academic Self-concept	0.10	4.62⁎⁎		0.10	4.86⁎⁎
	F(4,1921) = 377.51; p = 0.000; R2 = 0.44, Fchange(3,1921) = 424.94, ΔR2 = 0.37; p = 0.000			F(4,1921) = 353.73; p = 0.000; R2 = 0.42, Fchange(3,1921) = 411.68, ΔR2 = 0.37; p = 0.000
3rd step: Maths added
Classroom Environment	0.03	1.99 (♦)	0.08	-0.02	-1.22	0.06
Maths Self-efficacy	0.25	11.42⁎⁎	0.41	0.22	9.80⁎⁎	0.41
Maths Interest	0.05	2.63⁎ (♦)	0.22	0.07	3.72⁎⁎	0.20
Academic Self-concept	0.04	2.34⁎	0.21	0.05	2.77⁎	0.21
Maths Web-test	0.54	28.52⁎⁎	0.55	–	–
GCSE Maths	–	–		0.55	28.52⁎⁎	0.55
	F(5,1920) = 592.38; p = 0.000; R2 = 0.61, Fchange(1,1920) = 818.33, ΔR2 = 0.17; p = 0.000			F(5,1920) = 565.31; p = 0.000; R2 = 0.59, Fchange(1,1920) = 813.33, ΔR2 = 0.17; p = 0.000

The table reports results of analyses conducted on half of the sample constituted by one randomly selected twin in each pair. The analyses replicated in the sample of the co-twins are very similar. The symbol (♦) indicates when significance is discrepant in the two samples; R² reports the adjusted value of the percentage of variance explained in the model. ΔR² represents the change in R² in the new step, resulting by the addition of the variables. Only results significant in both samples are reported significant in the overall analyses. The variables added in the model are noted with bold characters.

^⁎⁎p < 0.001.

^⁎p ≤ 0.05.