Evaluation is a major function that a teacher has to perform. It could be of the formative sort wherein you evaluate during the course of teaching. Evaluation could be summative wherein you evaluate after you have finished teaching.To understand techniques of evaluation you may see http://www.egyankosh.ac.in/bitstream/123456789/25729/1/Unit5.pdf
You may read http://www.cs.umd.edu/class/fall2002/cmsc434-0201/notes6.pdf
For more on informal assessment see http://www.finchpark.com/courses/assess/informal.htm
Do check http://www.ntlf.com/html/lib/bib/assess.htm for some good ideas.