ANSWER: Proposition 21

From what I was able to find, it seems there is a dearth of analysis on Prop 21 since it passed in 2000.

Some of the recent statistics on crime in California make some mention of Prop 21. Also, looking at the statistics, you can try to make some inferences yourself on how Prop 21 has affected crime stats.

http://ag.ca.gov/cjsc/publications/misc/jj05/preface.pdf
This is the most recent publication from the Attorney General's office in California on juvenile crime. The 2003 report
http://ag.ca.gov/cjsc/publications/misc/jj03/preface.pdf
mentions Prop 21 in the preface.

Statistics from the California Department of Corrections and Rehabilitation:
http://www.cya.ca.gov/DivisionsBoards/AOAP/FactsFigures.html

The Center on Juvenile and Criminal Justice has a section on Prop 21, although not too much recent information:
http://www.cjcj.org/jjic/prop_21.php

The 2005 annual report from the Coalition for Juvenile Justice focused on trying children as adults. The report is $10 to order. It doesn't seem that many libraries have copies, but there is some free useful information on the site (including ordering information):
http://www.juvjustice.org/publications/2005ar.html
Childhood of Trial: The Failure of Trying and Sentencing Youth in Adult Criminal Court

Human Rights Watch and Amnesty International released a report on trying and sentencing children as adults in the US:
http://hrw.org/reports/2005/us1005/

This is a paper that addressed the problems of trying and sentencing kids as adults, and discusses California
http://www-rcf.usc.edu/~idjlaw/PDF/14-1/9-%20Angell-Final.pdf

This is another paper similar to the above:
http://law.bepress.com/cgi/viewcontent.cgi?article=1047&context=villanovalwps

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I would suggest visiting your local law library, or contacting one of the above organizations directly. They might have some resources available in print.