A cognate is a word that sounds similar or is spelled similarly in two languages: acceleration (Spanish) and acceleration (English) are cognates.
If you are a science and know German, you could have a German student in your class say the German word for mammal (Säugetier=suckling animal) and use that to help understanding of the term. Similarly with:
Or if you are a maths teacher:
Or a geography teacher:
Not only does this help all students learn new terms, but it also validates the native language and the presence of the ESL student in your class. Even if you know only English, you could ask from time to time what the word is in ESL student's mother-tongue - it may very well be a cognate. In any case, hearing the word in their own language often helps other students in the class to understand something they were struggling with.
Note, however, that cognate languages such as English and German have the problem of false friends. These are words that are spelled or sound the same, but which have different meanings in the two languages. For example:
Teachers need to be aware of the danger of false friends, but generally they are more commonly found in everyday language than in subject-specific vocabulary.