I like your idea to give students benchmark tests that they can retake to show improvement and mastery. I worked with some ELL students at an afterschool program and they really struggled with math and science vocabulary. Their science teacher gave weekly vocabulary quizzes and expected them to keep pace with the rest of the class with little accommodation. The students enjoyed the content by grew extremely frustrated with the class simply because they couldn't handle the heavy vocab load. It looks like you have provided several ways for students to learn and practice new vocabulary. I recently read a posting about programs to help students with math vocabulary. Someone provided a link to a website called Spelling City (http://www.spellingcity.com/). It seems useful and allows users to create personalized vocabulary games.
Have you students type the words into http://www.spellingcity.com/
In this site, the student type in the words and can chose to test their spelling, vocabulary, play a game or "teach me". Depending on the level of English speaking students it may be too difficult or too easy. But have your students try it because I know my students really enjoy it!