Could you recommend a beginner project for soldering practice or similar?

I have a few microcontrollers that have no smoke in them, that I keep around for pin alignment.

As a party trick, at the end, use a similar technique to show them how to line up pin headers before soldering. Stick headers into breadboard at the required spacing, place protoboard on top, and solder.   

Then demonstrate the Arduino Uno shield anomaly

Great perf-board suggestion b_d. I might use it the next time I pull together a soldering exercise. A once used four people in a soldering exercise for a RoadTest some years ago.

I've bought some cool little kits off places like AliExpress or Temu for a few dollars that give a little bit of soldering practice and you end up with a cool finished project.

There are some good tutorials and guides out there. For example, Adafruit has a tutorial PDF you might want to check out. It appears to be quite comprehensive. 
https://cdn-learn.adafruit.com/downloads/pdf/adafruit-guide-excellent-soldering.pdf

Perhaps this would be a good one to mention ?

Fundamentals of Soldering Member Videos

https://community.element14.com/products/roadtest/w/documents/27933/fundamentals-of-soldering-member-videos

Welcome to element14.

We have all sorts of members so feel free to ask questions.

For soldering skills, start with just tinning wires.

That will teach you about holding the iron against the material and watch how the heat transfer process works.

When you see the solder flow from the iron to the wire, you will know when you have made a good connection.

Now that sounds familiar. We were given 36-way solder tagboard in college. Only time I've ever used it.

A alternative to this may be to get some stripboard/protoboard, a roll of tinned copper wire, some side cutters and a breadboard.

Place the stripboard/protoboard copper side up on top of the breadboard, cut off a short length of wire and push it through a hole in the stripboard and into a hole in the breadboard underneath. The breadboard will hold it in place vertically.

Now solder the end of the wire to the copper track.

Experiment with different tip placements, heating times until it becomes a smooth process. 

Repeat this until you have filled the stripboard holes with wire. You should see your solder joints start to improve as you practise this.

Try different thicknesses of wire, solder, iron tips, and heat settings as you progress.

thankyou very much

thankyou I really apreciate your tip

in 30 year of teaching folks to solder, only 2 ever were masterful in a day. 
its more likely, youre going to destroy some stuff, so skip right to it.
find some old electronics. start by pulling parts. can you remove a capacitor without destroying it, or the pads?
can you ID the parts youre removing before you remove them?
once the components are removed, can you still identify them?

yt aint gonna teach no one pattern recognition, or manual dexterity,
which are the exact skills proficiency require. 

dont start with potted electronics. 
i youre note sure what a part is, look it up, but if you cant find it, who cares we're just partsing out waste boards anyway. 


ideally, you get so you can remove, all the parts, then replace or reassemble devices. 

The harder part of this method is commercial electronics use solder with a higher melting point.

if you go with a more conventional method, theyll say pick some simple lower part complexity project, 
use lead solder because it melts easy, learn to pool, and bead the solder,

I taught myself to solder in 1992, when I was 12, after figuring out that while my dad could solder, he as couldn't teach me to solder. 
there are 1000 methods, and strategies, it might be interesting to see what you come up with. 

I think you should teach us to solder. 
go get a toaster oven.