The Religion of the Educated Classes Revisited: New Religions, the Nonreligious, and Educational Levels - James R. Lewis
The measure Lewis uses to compare religious groups is what percentage of members of the respective religions have graduated from college.
The findings are similar to the results of the Pew Survey in the United States. However they are based on census results of the whole population and are therefore not extrapolated figures or subject to margin of error as the Pew Survey was. It's therefore a much more robust evidence base for demonstrating that JWs are the least educated religious group in Canada, Australia and New Zealand.
Only 6.3% of Jehovah's Witnesses in Canada have completed college, compared with 20.9% of the general population (Catholics 17.7%). In Australia 5.33% of JWs have graduated from college, compared with the national average of 14.5% (Catholics 19.09%). And in New Zealand the respective figures are 4.94% and 14.17% (Catholics 18.7%).
The only other religious group that comes anywhere close to JWs in lack of education is Satanism is New Zealand. But they are a relatively small religious group (just over 1000 members) and marginally more adult Satanists than JWs have a college degree.
Members of all other religious groups are significantly more likely than JWs to have completed college. This indicates a high level of obedience among JWs to the leadership's direction to avoid higher education. Especially when you consider that of the few JWs who have gone to college, many may have done so before conversion, indicating that only a tiny percentage of those who are brought up as JWs manage to go to college while remaining in the religion.