The importance of positive teacher-student relationships has been widely documented (see The Best Resources On The Importance Of Building Positive Relationships With Students).

A new meta-analysis has tried to make more direct connections between those relationships and student academic achievement, and to identify its effects by grade level and by subject.

Teacher-student relationship and academic achievement in China: Evidence from a three-level meta-analysis found that a positive teacher-student relationship had the greatest impact on academic achievement in high school, followed by middle school.

In terms of subjects, it had the biggest impact in English, followed by Math.

The study focused on Chinese students, though, so that context might not make the findings universal. Since English is not the home language in China, I think a case could be made that the equivalent here in the U.S. would be in ELL classes.