Publishers in the educational market are as varied as the people who buy their books.
Some of them are large, like Scholastic, which is practically an empire in the educational market.
Capstone is a conglomerate of publishing imprints that includes, Capstone Press, Compass Point, Heinemann-Raintree, Picture Windows, and Stone Arch. Their spring paperback catalog featured 398 new titles. That doesn’t include their spring library titles.
Some are small, like Creative Company or Norwood House who publishes about 75 books in a year.
Some are family owned and operated like Mitchell Lane or Crabtree.
Some have a stable of writers and hand out assignments only, some use book packagers, some accept manuscripts, some accept queries and/or proposals.
Every publisher in this market has a personality, a goal they want to achieve in their books, a focus or method of presentation.
Mitchell Lanes publishes biographies, almost exclusively. Stone Arch publishes fiction. Bearport promotes their books as narrative nonfiction. Picture Windows uses illustrations rather than photographs. Teacher Created Materials publishes paperback only. Bellwether publishes library bound books written on an incremental reading scale similar to leveled readers. Saddleback caters to the struggling learner in middle and high school. Scobre’s writers are all twenty-somethings.
The place to learn their personality is in their catalog. You can get a feel for their books online, and you should read some of their actual books if at all possible, but I like to hold that catalog in my hands. The way it’s organized and the information included will tell you a lot about a publisher. You can request a catalog at most publisher websites.
I've never had the privilege of going to the big bookseller conferences, but if you live near where one is being held, take advantage of it. Talk to the publisher reps. It's another good way to learn about a publishing house.