For the Concordia Itl. School I found this:

http://www.expatexchange.com/rspnet.cfm?add=ok&rid=62&answerid=24143&networkid=31&start=24143

It doesn't give a lot but at least there is some small info.

As for Shanghai United International School well....This board does have some things to say such as this:

http://www.eslteachersboard.com/cgi-bin/review/index.pl?read=26632

and this:

http://www.eslteachersboard.com/cgi-bin/review/index.pl?read=42653

and this...

http://www.eslteachersboard.com/cgi-bin/review/index.pl?read=32338

As well as the whole thread of "great" comments on how this "school" rips people off.

Dulwich had this:

http://www.internationalschoolsreview.com/international-schools/dulwich-college.htm

and this: http://www.expatexchange.com/rspnet.cfm?rid=62&answerid=16123&networkid=31&start=16123

British International School yielded a bit more promise as this came up:

http://top.at0086.com/International-Schools/Best-10-International-Schools-in-China.html

and this information page: http://www.english-schools.org/china/british-international-school-shanghai.htm

If you absolutely had to pick one, from the preliminary research I would go for the 4th one. But all in all a better option would be to send your kids back home. Most if not all "International Schools" still have MONEY as their bottom line, not quality of education. Hope this helps.