I am getting ready to knit a slouchy beanie, but the pattern calls for worsted yarn and my yarn is sport weight.
How do I allow for this?
The difference between sport and worsted weight yarn is not that much. I suggest you to make your swatch and measure your gauge. If you are lucky, you may not have to make any adjusment to the directions on your pattern. If you find out you have just a few stitches less to have the same number of stitches your pattern calls for, you can try the following needles number down. On the contrary, if you have a few more stitches you can try with the next needles number up. This is a suggestion you'll always find in every pattern although you have the yarn they call for.
Patience, persistence and love are the main ingredients for wonderful knittings.
I agree, your swatch will tell you how to use the sport weight yarn for this beret. Once you know the sts per inch that you're getting and can judge the knit fabric (too tight, too loose) you'll have an idea of how to proceed. You can always add extra sts into the pattern if necessary.