The part that got the most coverage was their claim that government data showed that more teens "entered treatment for marijuana abuse and dependence than for any other drug including alcohol."

See
The AP Gives Califano A Free Ride For Prohibitionist Propaganda

This is a classic example of lying with numbers that almost say what they claim, but may mean something else altogether:

Of the nearly 181,784 teens and children who entered treatment in 1996, nearly half -- 48.2% or 87,687-- were admitted for abuse or addiction to marijuana alone: 19.3% (35,069) were admitted for alcohol with a secondary drug; 11.9% (21,594) for alcohol alone; 2.9 % (5,323) for smoked cocaine, 2.4% for methamphetamines (4,354); and 2.3% (4,166) for heroin). More than half the teens in treatment for marijuana were between the ages of 15 and 17."
See
Califano Says, "Teens who smoke marijuana are playing a dangerous game of Russian roulette."
And Other Brilliant Insights.
First, it should be obvious that marijuana can be misused or abused by anyone, and young people are almost certainly at greater risk than adults when they use any psychoactive substance. The Dutch data clearly demonstrates that a small percentage of marijuana users seek treatment on their own.
See
"Tremendous Increase In The Number Of Dutch Cannabis Users Asking For Help"
Swedish Prohibitionists Claim

Second, the prevalence of a problem does not measure its severity.

Marijuana is by far the most widely used illicit substance, so it would hardly be surprising that more people seek treatment for it than for less commonly used substances, which are much more dangerous. For most teens, the drugs that they can most easily find, alcohol, tobacco and marijuana, will be those which they will tend to abuse. On the other hand, very few are treated for PCP abuse. Would even Joe Califano claim that marijuana is as dangerous as PCP?

As for the claim that more teens "enter treatment" for marijuana than alcohol, it should also be obvious that alcohol is both more dangerous for the individual and more widely "abused" than is marijuana. So these numbers really tell us that our "treatment" priorities are badly imbalanced. One indication of this is the fact that more than half of those being "treated" for marijuana also report "using" alcohol.
See
If Telling The Truth About Binge Drinking Works Better Than "Hardline Crackdowns." What About Marijuana?

Now let’s look at the source of the CASA data on "TEDS" Treatment Episode Data Set :
(A "treatment episode" is an admission to some sort of "treatment" program.)

SAMHSA Marijuana Data

From http://www.samhsa.gov/oas/teds/teds96htm/MJ.HTM on July 15, 1999:

Secondary use of alcohol was reported by 59 percent of admissions for primary marijuana abuse (Table3.8)"
(There are hyperlinks to all of the tables on the SAMHSA TEDS page.)

In short, half of all those in "treatment" for marijuana were sent by the courts. They may or may not have needed "treatment" – but there is no way of knowing. The teens may or may not have been sent by the courts at the same ratio, but it may well have been at a higher rate because teens have very few rights.Also, it may well be that others were sent by schools, or by their parents, whether or not they really had a problem.

Moreover, most of them – 59% -- reported "secondary" use of alcohol. (No, these numbers do not match the CASA numbers.) How is the determination made that marijuana was the primary problem for them?

In a context in which any use of marijuana is classified as "abuse," it is very difficult to know what the data really mean.

Also note that most of those in these programs started marijuana use at a very early age. Consequently, these numbers tell us very little about the risks associated with later onset marijuana use by teens. Certainly, very early use would seem to be more problematic, and perhaps indicative of other problems, such as parental neglect.

In reality, the only certain conclusion from this data is that marijuana prohibition is a spectacular failure at keeping even very young children from getting and misusing marijuana. As the CASA report says, "CASA’s 1998 teen survey reported that 19% of middle school students and 45% of high school students say they can buy marijuana in an hour or less."