Home schooling is as effective (or not) as the quality of the teachers involved and the abilities and engagement of the students.
The problem with most JW home schoolers is that they do it for the wrong reasons--to avoid socializing with people with differing beliefs--and the lack of qualifications of the "teachers" which are often the JW kids' parents, people whom themselves are usually not highly educated.
For those interested in a deeper dive, here is a link to a very informative paper on the pros and cons of home schooling:
- HOME SCHOOLED VS. PUBLIC SCHOOLED
SPECIFIC DIFFERENCES IN THE EDUCATIONAL OUTCOMES OF THOSE STUDENTS WHO ARE HOME SCHOOLED VS. STUDENTS IN A TRADITIONAL SCHOOL SETTING by Kathi Moreau