The effectiveness of work-based learning (WBL) was examined in an exploratory study of WBL in three different programs in Los Angeles: a transportation career academy (TCAP), medical magnet high school (MMHS), and school-based enterprise (SBE). Data were collected from the following sources: surveys examining students' WBL experience; interviews with teachers, mentors, employers, and others associated with the programs; observations of the students at work; and in-depth student interviews. The SBE gave the most latitude to students with respect to choosing work tasks and even work times, whereas work at the other two sites was more closely monitored and scheduled. The MMHS and TCAP incorporated formal evaluation procedures between the worksite and the school. Training for the TCAP students followed a "show and tell" model, whereas the MMHS students were apprentices in a university science laboratory where teaching was embedded in nearly every activity. The SBE used a talented mentor pool, outside conferences, free advice from experts, and opportunities to practice in a fail-safe environment. No site developed students' problem-solving skills around substantive, technical matters. The TCAP and MMHS programs had explicit career awareness or exploration goals. All three sites incorporated structural features for connecting school and work. (Contains 58 references.) (MN)