I'll absolutely second this. I know kids who went to tons of prep classes for literally years. I had a friend whose parents paid for her to attend SAT prep summer camp for about a month every summer starting in sixth grade. Most of them did fine, but their scores were commensurate with that you'd expect from their report cards. I didn't study much and did very well. The students who did very well were mostly either those who were high-achieving in other respects or those who worked very, very hard. E.g. I know someone who wasn't particularly academically outstanding but got a perfect score with study, practice books only, no expensive classes.