One of the challenges the church faces in the 21st century is the incorporation of teenagers and young adults in Sunday services. We have become adept at running 'great children's programmes', so drawing parents with young children into the Sunday life of a parish has proven a successful strategy in many parishes. But the success of these programmes has been based on running them in the parish hall as a parallel to the service in the church which - understandably - has become an adult-oriented service. The weak point of this strategy (in my observation)is the gulf between the children's programme and the adult service so that when children turn teenagers they feel there is no place for them. (Of course there can be a place for them, e.g. by running a teenage parallel programme; its just that many parishes are exhausted in terms of people resources running a children's programme on Sundays).
One way to overcome this weak point is to make the gulf between 'adult church' and 'children's church' as small as possible. There are a range of ways to do this (which may be addressed in a future posting), and a key to one way of doing this ('all age' or 'inter generational' worship) is to offer one and only one sermon or talk but to ensure that this communication is inclusive of all ages.
Over the years I have developed a little experience in this kind of communication. What I have found helpful is developing a style of speaking which (a) relies on as few notes as possible (b) involves interaction with the congregation (through questions/answers/reflections) and (c) takes advantage of technology (particularly using a radio microphone).