The single biggest predictor of high academic achievement is socioeconomic status of parents.
"The single biggest predictor of achievement is achievement"
Plenty of people don't define academic success as achievement. A lot of blue collar communities consider other things as being successful.
In particular, from the subsection "SES and Academic Achievement":
1. Children from low-SES environments acquire language skills more slowly, exhibit delayed letter recognition and phonological awareness, and are at risk for reading difficulties (Aikens & Barbarin, 2008).
2. Children with higher SES backgrounds were more likely to be proficient on tasks of addition, subtraction, ordinal sequencing, and math word problems than children with lower SES backgrounds (Coley, 2002).
3. Students from low-SES schools entered high school 3.3 grade levels behind students from higher SES schools. In addition, students from the low-SES groups learned less over 4 years than children from higher SES groups, graduating 4.3 grade levels behind those of higher SES groups (Palardy, 2008).
4. In 2007, the high school dropout rate among persons 16- 24 years old was highest in low-income families (16.7%) as compared to high-income families (3.2%) (National Center for Education Statistics, 2008).