I've been having a lot of fun in this game with the chief. It seems like when he directs work, a lot more gets done. He's also good with healing and with impregnating the women. I have a couple of questions:

1. When he lectures, is anyone gaining in their skills? I took one of my no skill people to see if they gained in any one area and they didn't.

2. When he points out rare objects, how do you know where to look? I get a bunch of coral and stuff that's already appeared and maybe one new item. Am I missing something?

1. Lecturing doesn't give any skill.

2. The rare collectibles appear anywhere where they are usually found, except feathers. (they can appear anywhere) :P

What's the point of lecturing if the students aren't getting anything out of it?

It helps when you need to do something like make sure nobody is standing on any collectibles. Not much use. If you lecture on the kids and have level 2 leadership, the kids will get a bit of skill after there is a sparkle above their heads.

To lecture children, drop him on a child; this is to teach them skills. Lecturing the tribe is just to gather them together.

There's no way to know where to look for collectibles, but just knowing they're there should give you plenty of time to find it.

Do NOT pause to look for collectibles. By doing this, you may lose it altogether. It may take up to a minute or two for the rare collectible to appear. Since collectibles do not appear or disappear while paused, if you are paused at this time, it's gone.

I have had kids gain experience after an general all ages session of lecturing.
Probably more so that when it is only the kids.

As some have said elsewhere you notice a star appear above their head.

I'm not sure why you saw an improvement here, but an all-ages lecture does not grant anybody any skills. If this has happened to you, this is a glitch. (Or a lecture was interrupted by a teaching session - the older villagers will still hang around as if attending the interrupted lecture.)

Note the leadership tech screen - the chief only gets the ability to teach at tech 2, and he can only teach once every 24 hours. However, a general lecture can be given without the tech requirement, and he can also lecture repeatedly when he will flatly refuse to teach more than once every 24 real-time hours.