The levels vary, and something that catches my attention the most is the notion of the 'Token youth'. This is where a young person may be added to the group for their opinions, but in reality are only there just so the group can say that they had a youth represented there. Or at times they might not feel engaged enough to be a true representative in the group...
This is great for seeing where young people currently fit in within a group and where and how you would like them to be involved. Of course, we can also apply this to other categories of individuals which can be involved such as the elderly involvement in a group.
So here's a copy of the ladder borrowed from http://www.freechild.org/ladder.htm, where they detail each of these levels or 'rungs' as they call it in more detail, where:
Rung 8: Young people and adults share decision making
Rung 7: Young people lead and initiate action
Rung 6: Adult-initiated, shared decisions with young people
Rung 5: Young people consulted and informed
Rung 4: Young people assigned and informed
Rung 3: Young people are tokenised*
Rung 2: Young people as decoration*
Rung 1: Young people are manipulated*
*Please note that the last three rungs are non-participation by young people.
This overall is adapted from Hart, R (1992). Children's Participation from Tokenism to Citzenship. Florence: UNICEF Innocenti Research Centre.