Years ago in about 1975, I was an enthusiastic LÜK learner. LÜK stands for learning, practicing, assessing and is actually a learning system for 3 to 15 year olds, but I was also able to use it while teaching German at a Japanese university as well as for an evening class for adults.
The main item of the LÜK learning system is a control / assessment unit: a flat plastic box in B5 format which can opened. The bottom of the box is split into 24 squares onto which you can place 24 tiles. The idea is that you solve the multiple choice questions in the booklets. For instance, you take tile number one and answer question number one. Behind the correct answer you will find another number, say 17, and that is the number of the square onto which you then place tile number one, and so on until all 24 questions have been answered. Once you have placed all the tiles into the box you close it, turn it over and open it again. The backs of the tiles make up one of the more than 100 possible patterns. If the pattern does not fit, you haven't answered the matching question correctly. If, once you have answered the question correctly, you find that there is already a tile on the correct square, then you have to turn your mind to those questions again.

There are 4 booklets for German as a foreign language. Booklets 1 and 2 are for vocabulary and booklets are for grammar. I found that not all of the exercises are suitable for lessons at a Japanese university. Sometimes the grammar questions are to easy or there are too many words not known.
Meanwhile, I have devised my own exercises, which is relatively easy. You retain the structure, ie which answers have to be correct and replace the questions and answers by your own.
Almost all of my students are thrilled with LÜK. The books are visually appealing and the excitement when turning over the control unit is always great. It is a good idea to let two students work together on one unit, that seems to be more fun for them and it's cheaper. Each student (or pair) needs one control unit which costs 16,50€. The booklets cost 5,70€ each. I was able to order everything without difficulty through the library of my state university, because even the control units have an ISBN number.