It is called "ELL" now not "ESL". There are five levels of ELL. At the end of each school year, the ELL teacher will assess the level of the student. If the student could pass the assessment, he could promote to the next level the next school year. However, if he could not pass the assessment, he would remain in the same level the next school year. Therefore, how long it takes for a student to complete the ELL really depends on the student himself.