I also remove the paper after the block is finished and before sewing any blocks together. Never had a problem doing it this way.

Here's a thought...probably only good for scrappy, string. Example: 5x5 block. Paper cut to that size, but when you finish block and trim fabric, trim to 5 1/2 x 5 1/2... Then you can leave paper in for stability, but the seam allwanes are paper free...I use old phone books and I get prospectuses from investments regularly...don't read them, but paper is thin enough to be used.

I have made several string blocks and have not used paper for a foundation. I use a thin interfacing as my foundation to sew my strips. I do not like tearing the paper off, I can leave the thin interfacing in as it does not ad weight to the block and saves me from all that extra work of trying to get the papers removed.

If I had sharp points or needed perfectly line up of the blocks, I leave the paper in until after I stitch the blocks together.

If you need the stability, rather than removing all of the paper, just tear off the corners or edges that might get caught under a seam.

Often with paper piecing ( not string blocks) you are matching points or elements when joining so the papers are generally used to assist with that- if the instructor is a ( paper piecer) that practice is probably the norm for her. If just making random string blocks with no concern of anything matching up it would be fine to remove the papers ahead of time. The papers do assist in keeping many edges stable for construction but it's your choice. Personally I hate removing papers from blocks like string blocks so I use thin inexpensive muslin for a foundation so I can just leave it in.

I have used well-used softener sheets. After they've been through the laundry enough times, they are soft enough but still stable to use for foundation. Simply press them flat and leave them in your quilt.

That's how I have done my string blocks...and since we live in Maine, I'm not worried about the extra fabric to make the quilt heavier.

I'm just finishing a string quilt and didn't use paper but I did use dryer sheets. No need to rip those off at all and every time I have had to iron them, the aroma is lovely.

I usually don't remove until the top is complete - it's a pain but worth waiting after putting so much time and effort into the project.