-w - Search whole word
-l - Only print the filenames of matching files
-r - Recurse into subdirectories
ack -lrw '< MySuperClassName' --ignore-dir={app/assets,log,spec,vendor,public,coverage,config}
You can chain this to xargs to open all the matching file for editing like this:
ack -lrw '< MySuperClassName' --ignore-dir={app/assets,log,spec,vendor,public,coverage,config} | xargs mate