There are multiple aspects: vocabulary, speed, and comprehension.
- Vocabulary. The typical university student knows 15 to 20,000 words, plus about 500 common academic words, plus a few hundred specialized academic words related to their studies (economics, history, ...). Learning more vocabulary is important. Some English for Academic Purposes (EAP) classes help students learn the 3000 most common words and the 570 words from the Academic Word List (AWL). (Do a google search on Coxhead and AWL)
- Speed. The typical university student reads at 300-400 words per minute for general reading (such as newspapers or novels). Immigrants in my ESL classes usually read at 50-100 words per minute. Some EAP classes help the student reach 300 words per minute. (In university, I had six hours of reading a day; at 100 words a minute, it would have 18 hours of reading per day; obviously impossible.)
- Comprehension. Simply reading is not enough. In high school, students (supposedly) learn to write a summary of the main points and to connect the main points to the world in general or to their life. If students can't write a summary or can't connect the material to the world, then they haven't understood the material.
Good luck to you.