I am in need of a reference to a "bachelor thesis" but the file bxml-apa.mkiv only provides "phdthesis" as a possibility. Adding the following code to bxml-apa.mkiv doesn't work or is not enough to add the "bachelorthesis" as an extra. 
I did search for "phdthesis" in the ConTeXt base files and was found once: in the bxml-apa.mkiv file.

How to?

\startxmlsetups bibtex:apa:bachelorthesis
   \setvariables[bibtex:temp][label=Bachelor thesis]
   \bibxmlsetup{bibtex:apa:common:thesis}
\stopxmlsetups

used in the .bib file as:

@bachelorthesis{rijneveld:13,
Author = {A. Author},
School = {Excellent University},
Title = {{How the Dutch.}},
Year = {2013}}

 Hans van der Meer