Unlimited access to all learning material for a flat monthly subscription fee. Unlimited = read all*; Unlimited+ = read and practice all*. Certification need payments per course.
Use short diagnostics and targeted follow-ups to find the few skills causing most mistakes. Then intervene early with focused practice and feedback.
A small diagnostic can reveal a lot when it targets prerequisites.
Most learners are blocked by a small number of missing skills. Fix those first and progress accelerates.