Rule of Thumb

Number in Youth ministry should be 10% of Sunday attendance.

According to a church planting/church growth specialist that I know, the quickest measure of a church's youth ministry is to compare the number in the youth ministry to the total number in attendance on Sunday mornings. While exact demographics will vary between communities, in general one can assume that teenagers comprise approximately 10% of the population. Therefore, an average church should also include about 10% teenagers as well.

According to 2000 US Census

Age	% of Population
Age 0-4	6.8%
Age 5-9	7.3%
Age 10-14	7.3%
Age 15-19	7.2%

So Ages 10-19 together comprise 14.5% of the general population. Assuming that this 14.5% is evenly distributed across the 10 year range (1.45%/yr), we could calculate that the 7 year range from 6th grade through 12th grade would equal 10.15%. Depending on where you draw the lines for the upper and lower ranges of "Youth Group"  you can make your own determination about the exact percentages... but it seems to me that 10% is in fact a good figure to use as a "rule of thumb."