弟子 (deshi) is also a commonly used word. It also means apprentice (魔法使いの弟子 = The Sorcerer's Apprentice). It carries a bit of more weight with respect to the relationship with the teacher/master. So if you were talking about a master carpenter who took on an apprentice in order for the senior carpenter to pass along skills and induct the junior carpenter into the trade you might use this word. It is also used as a direct translation of the word "disciple" - and so it can be used in a religious context, but it isn't limited to that context. I guess it implies a transmission not only of skills, but also of a way of thinking, a way of life. So it wouldn't be appropriate for relationships that are strictly boss/employee or teacher/student relationships.