may be you can go to Wah Shing Mandarin education centre, i think it is professional and i can learn mandarin effectively. There is the summer course, if you are interested, may be you can send e-mail to them and get more information about it.
I know they have summer courses now~may be u can ask for any information about it.
here is the e-mail:
wahshing_mandarin@hotmail.com