I wouldn't mind reading a letter from a student, but if the only letter covering teaching were from a student, it would definitely raise eyebrows.

It will also give someone on the committee an easy way to strongly object to you, and for most positions that's enough to bring an end to your hopes.

On a more philosophical note, your students are surely most familiar with your teaching, but they are not the best qualified to judge it. A student is likely unable to assess the depth of your knowledge, the ease of your course, or how you deal with problem students and complaints. All of these will be of supreme importance to the department looking to hire.