My kids both learned to read at 4 years old, without the aid of Watchtower publications. Everyone's brain develops differently. Are they receiving less of an education, without reading the WT magazines? YES! Their education is inferior, by JW standards.
IQ and academic tendencies will vary, inside and outside the organization. Simply focusing all of your energy and time on learning one specific skill, will limit you in other areas of your development. Take a genius and indoctrinate him into the society, and he will just be a well-spoken robot... which is the goal of the "education" you receive in the ministry school.
All JW's are studying at Watchtower U, and all study the same subject: Field Service.
All true servants of Jehovah ('s organization) share the same goals: Serve the Organization & Vindicate Jehovah's Name.
Their "education" level is measured and recognized by their degree earned at WTU: Publisher, Pioneer, Ministerial Servant, Overseer, etc...
Intelligence and education are not the same thing. There are many intelligent people being manipulated by this high-control society. They believe what they say about themselves. Since their goals are to serve the society and earn Degrees in Service, they are correct. Their education is far more valuable than any college degree.
If you are going to measure by worldly standards, you will come to a different conclusion.
Truth is relative to the situation.
Once programmed sufficiently, after years of schooling at WTU, I think most JWs who actually pay attention in class are going to sound educated to those who are still sitting there listening to them talk.