Just this morning, I woke up to a comment on my TpT store which praised the circuit, but thought it would be better if it included an answer key. Once again, though I have it written in my product descriptions, I was forced to think critically about whether I should be including answer keys with my work. Maybe if I did, teachers would be better prepared? Maybe the students would learn more? Maybe I would have higher sales? Maybe. But maybe not. There are three main reasons I do not include answer keys with my circuits.
The first is, because of the format of the resource, the answers are embedded in the circuit. The students work the first problem, get the answer, and then hunt for the answer. When they find it, it reveals the second question. Students continue in this manner until they complete the circuit. So, I have already given the teachers and the students the answers.
Second, I do not want students purchasing answers keys! And neither do their teachers…
Finally, and most importantly… teachers need to work the circuits first to truly understand the unfolding of the idea. The majority of my circuits are not just worksheets but progressive paths through a skill or procedure. Teachers should be able to work the circuit in about 1/2 to 1/4 the time of their students. They should be able to recognize the “Ah ha”, “challenge” or “level up” moments to know when their students will get stuck and to anticipate how to get them unstuck without just giving them the answer. In this way, teachers will know how to maximize the use of this resource in their classroom. Should they give some notes first or is it more of a discovery circuit? Should they use it as a cooperative exercise or should it be an out-of-class assignment? These are questions only teachers can answer for themselves based on knowledge of their students, the length of their class period, etc.
But what if a teacher can’t answer a question or can’t find the answer or closes the circuit early (which means there is definitely a mistake somewhere)? Ask someone for help! If you are the only one at your school who is teaching calculus, e.g., then reach out to colleagues in other schools or reach out on social media or EMAIL ME at virginia.cornelius@gocommodores.org! I am happy to help!
Math, Teaching, and Teaching Math 
It never occurred to me that an answer key should be included. The best way to determine if an activity is appropriate for my students is to actually do it myself.
I know. People say things like, “It would save me time if I had the answer key,” and I want to reply, “How long can it possibly take for you to do a 20-question circuit?” But I bite my tongue (or sit on my hands).
A recent study found that if you give teachers good lesson plans, instead of PD, it will increase student achievement. Thanks to sites like TPT the end of useless PD is finally becoming a reality.
http://blogs.edweek.org/edweek/curriculum/2016/07/study_give_teachers_lesson_plans_not_professional_development.html
This just in: A student’s parent bought a circuit on Thursday night. The child’s circuit was due on Friday. I bet the parent was pretty surprised to not find the answer key. Should have read the product description!
I appreciate your comments above but I’d disagree. That is, I understand you want students to work through the material and not have them or parents just purchase the answer(s). However, most math teachers are already overburdened with 4-6 preps and hardly any time to work through every problem that we assign in all of our classes. Answers provide space for both teachers and students to confirm their work. And, in an ideal class, we want to work together but the pressure of standards and having to push through a curriculum in such a short amount of time do not always make this a picture of reality.
As someone who has taught for 28 years in both private and public high schools, I get it. You are busy. So am I. Use other resources if you don’t like they way mine are offered. Or, switch careers before you feel it’s too late and you must slog out the remaining “10” to reach retirement.
And yet here is someone doing 4-6 preps with two children who writes all these wonderful resources in her spare time. As she said, go find a different resource and watch out for the burn out.
Well, there isn’t much spare time. I just write circuits to avoid cleaning the house. I knit in my spare time.