Parents have asked me which is better, group prep sessions or private tutoring. My answer: It's all about money.
Group test prep is less expensive for parents than private tutoring. Group test prep is more lucrative for test prep companies.
Private tutoring is more expensive for parents and less lucrative than group test prep for tutoring companies.
How do you decide which is better? Figure out what's better for the student. Many students need individual attention. A group setting can not provide this.
So, It's all about money - but money should not be the decisive factor.