Teach Math In English Or Student's Native Language: What works best for English Language Learners?

Would an elementary English Language Learner student make more progress learning math in their native language or their second language?


For the past 16 years, I am always amazed what the brain is able to do to overcome language obstacles.   For the past 13 years, I have taught bilingual students and 3 years, I have taught monolingual students Spanish.  Elementary students are able to grasp a second language rather quickly.  When I teach math to my 1st grade English Language Learners, I speak English in complete sentences and expect that my students, through time and much practice, are able to speak English in complete sentences and use correct vocabulary words to verbally explain their understanding of the task at-hand.   

What are your thoughts and experiences with Math and the English Language Learners?