For the past 20 years, Minnesota kids who struggle in traditional public schools have had someplace else to go. Instead of giving up on education, students from ages 5 to 21 could attend an alternative school or an after-school or summer program.

However, as alternative education enrollment has grown from 4,000 to more than 150,000 over the years, more questions have been raised about the programs. The key issue: Are the kids really learning?

A state legislative auditor's study released Wednesday found mixed academic results overall. It also concluded that targeted, extended-time educational services show promising results.

That important finding makes the case for more investment by state and local school districts in similar efforts. Budget-stretched school districts have little capacity to add new programs, but they can look at reallocating existing funds for services that clearly bring students up to speed faster.

Here's why it's worth doing: The auditor's evaluation of test data for more than 35,000 students found that of the K-8 students who received targeted, extended services, about 30 percent had high growth on math and reading tests. Another 40 percent had medium growth levels, which means they were advancing at the same pace as students in traditional schools.

Those findings are consistent with other educational research that proves time-on-task matters. In fact, many of the countries that outperform American students on international tests have longer school days and years than the United States.

The Legislature authorized alternative programs in 1987 specifically to serve students who were at risk of not graduating. Today those programs include Area Learning Centers (ALCs), Alternative Learning Programs (ALPs), schools that have contracts with districts, and targeted, extended services. Under state rules, participating students must meet at least one of 12 at-risk criteria. The state provides about $140 million in additional funding for the targeted services.

However, the original law only allows districts with ALCs to receive funding for the targeted services. So an estimated quarter of all districts don't offer the extended-time programs. Officials say it would cost $20 million to $30 million to expand the effort to all districts. That relatively small investment (out of a $12 billion K-12 biennial budget) would pay for itself many times by turning out better-educated, taxpaying adults.

The academic success rate is less impressive for junior and senior high students. Many older students have lower test scores and poorer attendance -- not surprising, given that those issues are what makes them eligible for alternative programs. But the auditor's review indicated that when teens and young adults stick with the programs, they improve on those measures over time. For example, the researchers tracked a group of 12th-graders who had a graduation rate of 39 percent in 2006, but improved to 61 percent by 2009.

In surveys and face-to-face interviews with students, auditors found that many of the students would be engaged in unproductive, and sometimes illegal, activity were they not involved in an alternative program. That clearly points to the value of keeping teens and young adults involved in education.

In addition to suggesting expanded access to targeted services, the auditor wisely recommends stronger state oversight of the programs and calls for developing additional measures to evaluate alternative education student performance. Together, those actions can improve a system that serves a growing number of Minnesota kids.