That is a very well written answer I must say! Well, I for one didn't read the question properly and didn't pay attention to the research by objective part (sigh). Well this is what I wrote:

Ngos purpose for research: analysing social problems
Types of research methods: qualitative and quantitative
Ngos use qualitative; reasoning: more interactive less rigid
Types of research methods: overt and covert
Covert: tea room trade(example); ethical question mark; generally avoided but done when target population is inaccessible, field of study is sensitive: drug users for eg and if the researcher needs to protect his identity
Tea room trade : Research fraternity criticized the research technique: an invasion of privacy of the study sample but some researchers argued if no harm is done to the sample and research has social value it should be conducted.

Then I discussed the various designs employed by ngos:
1) in depth interviews: structured-semi structured-unstructured
2)focus group discussions
3) participant observation
4)questionnaires
5)case study method

I discussed the merits and demerits of each approach plus how the researcher can effectively use each design to improve his/her research. Maintaining a natural setting in the field during participant observation; avoiding asking leading questions; not letting one person dominate the fgd.

Then I mentioned which method would suit the social problem an ngo would study; participant observation if children are under study; ; understanding learning outcomes in different school settings(objective);
obtaining their consent is important
Fgds if the sample is large plus it gives insight into new behaviour
And mentioned similar examples for case study and interviews