So you needed the work and agreed to substitute teach today. Only now you're looking at the placement and starting to panic. If you've agreed to teach a class with a subject that is difficult for you, take a deep breath. Whether it is physics or calculus that has you concerned, there are some practical tips that will provide help for subs who dare to venture into these hard placements.
Get to School Early
Give yourself some extra time to focus on the teacher's plans before students start arriving and distractions abound. The teacher may have plans that don't require any special knowledge of the subject matter, which means you can relax. If it looks like you'll need to learn some basics, take the time to grab a textbook or search the Internet to give yourself a quick lesson.
Use Classroom Resources
Most classrooms have Internet access, and many even have smartboards. In your prep time, you may have found a website or a YouTube video of someone giving a mini lesson on today's topic. If it is relevant, understandable, and engaging, why not use it?
Involve Students in Cooperative Learning
The subject matter may not be your forte, but chances are there are many students in the classroom who catch on quickly. Use these students to your advantage and set up some cooperative learning groups. Put one student who knows the material in each group and assign work for the group to go through together. In the process of getting the assignment done, the students who excel will bring the others up to speed.
Review Past Material
If you feel like none of these are decent options, and there is just no way you can teach the material assigned, you can always help students review past material. This is still a good use of time because students will need to know the information for future tests, and solidifying learning on previous topics will make moving forward easier for them. In addition, a teacher will probably appreciate you not trying to teach something you don't know, conveying false information, and having to de-program and re-teach students the next day.
If you hesitate to take certain job placements because you think they may be too difficult for you, you're not alone. Most teachers don't expect subs to know higher-level course content anyway. Leave the teacher an honest note about what you did accomplish during the day, and give yourself a pat on the back for challenging yourself.