"SRAM XT derailleur" that one company & another brand model. Does the derailleur have a clutch? Is the chain sized properly. Falling off very often would be unusual unless he is riding pretty rough terrain. I ditched the guide (noise) for a narrowide front ring,

 

I ditched the guide (noise) for a narrowide front ring,

This crank uses Suntour's "zig zag" design, which is similar to MRP Wave (they use it on their cheap steel rings, and they license MRP Wave for their higher end alu rings). Suntour's proprietary direct mount interface isn't exactly easy to source 3rd party chainrings for. Mostly limited to what suntour sells., afaik.

I do wonder if the rear derailleur has a clutch, too. My first 1x drivetrain was 10spd with a clutch RD and a n/w chainring and I never dropped a chain on it.

I put a chain guide (top guide only) on my hardtail with 1x12 (clutched RD, n/w chainring) just because it was going to get pounded a little harder.

To the OP - can't recommend a chainguide unless we know what bike you have. Do you have ISCG or ISCG-05 frame mounts? How about a direct mount front derailleur bracket? Is your bottom bracket threaded or pressfit? Does the frame have a seat tube that something might be able to clamp onto?

Also, when I looked up your crank, I saw some reports of the chainring lockring loosening. Is this happening to your son's bike? If so, no chain guide in the world is going to fix that problem.

 

Sorry, it is SRAM X7 with a clutch. Not sure what I was thinking when I was typing. The chain falls even when jumping a curb. Tension and chain size is correct. We have total of 3 bikes with 1x10 setups and he's is the only one with a problem. I may try a narrow-wide chainring next.

 

I went through this issue when I converted to a 1x front. I was enlightened on this forum about narrow-wide chainrings, tried that, and my problem went away. I didn't (and still don't) have a clutched derailleur. Since going to a narrow-wide chainring, my chain has never jumped off.

edited: I do not use a chain guide with my narrow-wide chainring.

 

The bike has a Leader 27.5 frame. It was built and not store bought. I will double check when I get back home but there are no ISCG mounts on the frame. Seatpost tube would be the only way to mount a guide. The derailleur definitely has a clutch. What strange is that my younger son has a similar 1x10 system but based on the Shimano XT without a clutch but he never drops the chain. Maybe the difference is in the Suntour's chainring and the narrow-wide that my younger son has.

 

53mm chainline might have something to do with it. You can use a BB to ISCG adapter in place of the driveside BB spacer to mount a chain guide.

 

Thanks for all the replies. I took some photos of the system yesterday. The derailleur does have a clutch. Chainring states that it is "zigzag" - whatever that means. Forgot to ask my son if he noticed the chain dropping on high or low gear.