Watson, I think it depends on what you are going to focus on in your lesson. If you already know the basics and are learning design and technique, I would just take solid fabric so you can easily see your designs. If you are just learning the LA set up, functions and mover ability, I would take s simple lap quilt as you suggested and just have fun.

When I offer classes to learn my machine for future renting time we always start with muslin top & bottom because it's inexpensive and you can see what you are doing. Generally we would use a couple yards ( 44"X72") for practice and contrasting ( dark colored thread)
after learning the machine, threading, winding bobbins, cleaning, oiling, setting up stitch size, tension, etc. we would work on the muslin quilt top. First just some free motion to get the feel of it, learn to write on it, then drawing some designs to follow. Try a pantograph, put on the ruler base & try some ruler work.
My class is 4 hours. If after the practice quilt the student is comfortable and has time & brought a small pieced quilt we load that up and let them quilt it. A Queen would be too large for a practice quilt. For years if I wasn't working on a real quilt I had a muslin practice quilt loaded. My family & friends often stopped in & (played) practiced and I practiced on that quilt. We did all kinds of things with the finished ones, grandkids loved using fabric markers & coloring the stitched quilts. We cut them up, finished edges and donated them to the animal shelter, we made things with them.

When we bought our long arm, I went to Walmart and bought good red fabric and used some old batting. I had two 36" pieces of red and they ended up making nice dog beds.

Wow Watson....don't take your "good" quilt. Hold that until you get control of the machine. Take some charity quilts from your local guild. There are plenty of tops that need to be quilted and the recipients won't care if they are stippled, loop-d-loop or fancy custom quilting. It is great practice for you and you are also helping get a quilt closer to completion and donation for them!!

When I first longarmed I put together "practice pieces" made of the cheapest fabric I could find for top and bottom and a layer of batting. I usually made a piece two yards long and width of fabric. I used this to practice first time machine use and patterns before using on a real quilt. You can use all muslin but sometimes having a patterned fabric lets you practice working around the different motifs.
Later these practice pieces made good dog blankets. I'd cut them in pieces about 22 x 30 and turn over the edges to finish. Nothing fancy at all but my DIL loved them for her dogs. I also made a cover for my longarm from one of my practice pieces.

When I took my long arming class, we used a solid fabric and drew on "blocks" to work in. This is definitely what I would recommend for learning - you can see your stitching, you don't waste time piecing something that will have really random quilting, and solids are generally less expensive.

Depending on the length of the class, whether you have your own machine or share, and the techniques covered, a piece 1.5-2 yards by WOF is probably sufficient. A few people have suggested using a dark thread so you can see your stitching easily, but I would go with a lighter shade than your fabric - in my experience, it looks better, which is nice for a first attempt (even though I think I'm a fairly good quilter, my first long arming was rather shaky). As long as it isn't identical to the fabric,you will be able to see it well enough.

Good luck! I think you will love it!

When I find a great price on prequilted fabric, I always buy about three to four yards if it is a color combo that I like, as long as it is double sided. I do not buy one sided prequilted. I use my finds for gift bags, purse linings, baby blankets, baby snow suits, etc. if I were going to practice on a long arm, I would chose two versatile fabrics that I could do the same with. That way even though I might not love the whole thing, I could cut the parts I like into smaller projects, or use a solid on the back and some kind of print that I can follow with the quilting to practice control and following lines. I just can't think of a piece of fabric as "waste".

How about a 50 or 60 inch length of kid friendly printed fabric? When it is finished, it might be suitable for a charity quilt.

Depending on how much time you have for the lesson, I would caution against a great big top -- you might have to take it off the machine unfinished.

Definitely do not bring the top you care about. When I took my first lesson, it was a basic course that familiarized me enough with the machine that I would be allowed to rent time on it. They had a plain 1 yard piece of fabric that we loaded.

I think the key thing is take something you don't care if you ruin it. It is freeing and you won't be all tense worried about messing up on a top you care about.

I never did rent time at the shop because I realized immediately that LAing was the type of thing that took some practice and involves muscle memory. Two things I would never realize with sporadic rental time. So I bought an Innova. Here is a link to the very first quilt I did on it. I explained in this post how having a top I didn't care if I ruined allowed me try a lot of things most first time longarmers don't because they are afraid of messing up. When I did this quilt I only had the 1 class under my belt and had practiced on a one yard piece of fabric that we loaded when the LA was installed.

https://www.quiltingboard.com/pictur...rm-t77776.html

I like to use plain black fabric and a bright thread. It helps me see my stitches and make sure my tension is playing nicely.
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You might also consider an inexpensive print you may have on hand that has a pattern in it that you can follow. A flower print, paisley print or geometric print is always good to practice with your first time. Helps you get a feel for moving the machine while making a design.