An achievement test based on schema theory (S-Test) was developed on the passages comprising the English textbook taught at grade three in state high schools in Iran and administered concurrently with a validated and reliable Social Capital Scale (SCS) to four hundred seventy seven male and female participants. The Z-scores obtained on the S-Test were utilized to divide the participants into high, middle and low achievers. Among the ten factors underlying the SCS, i.e., "Self Volunteering," "Receptive Relatives," "Maternal Supervision," "Parental Monitoring," "Teacher Consultation," "Parental Expectation," "Parental Rapport," "Family Religiosity," "Helpful Others" and "Parent Availability," high achievers' "Family Religiosity" correlated significantly with their S-Test whereas a significant correlation was found between "Parental Monitoring" and S-Test for middle achievers, indicating that social capitals of these two ability groups function differently. The results also showed while middle achievers' scores on the semantic subtest of S-Test related significantly and "positively" to "Parental Monitoring," "Teacher Consultation" and "Family Religiosity," they correlated significantly but "negatively" with "Parental Expectation" and "Helpful Others" on the syntactic subtest. The semantic subtest also revealed the highest significant and negative relationship with low achievers' "Teacher Consultation." The findings are discussed and suggestions are made for future research.