Table 2.

Demographic materials of grade 8 and grade 4 students

Variables	Groups	Grade 8	Grade 4
Residence	City	54.59%	65.71%
	Rural region	45.41%	34.29%
Only child	Yes	59.74%/	47.23%
	Not	40.26%	52.77%
Left-behind child	Yes	7.6%	10.4%
	Not	92.4%	89.6%
Mothers' education	<College	93.42%	91.77%
	≧College	6.58%	8.23%
Father's education	<College	90.99%	93.77%
	≧College	9.01%	6.23%
Annual revenue	<60,000¥	71.7%	71.1%
	60,000¥-100,000¥	20.1%	20.3%
	>100,000¥	8.2%	8.6%

Note: ¥ = RMB.