The average rating in the U.S. is something like 1200. Some consider that the level of an adult with no chess training or tournament experience. One example might be a casual player that plays at lunch with a buddy. This type of player often will tell you they are “pretty good” or even “very good”. But, anyone with even modest tournament experience and training will generally clobber one without it.
For elementary school players I agree that 1000 is good and 1400 is really good. My daughter played about 300 scholastic and adult tournament games, winning many scholastic trophies (even one at the Nationals). She got just over 1100.
I have not played on Yahoo, but 2400 for regular over the board USCF ratings is the senior master level. These players also typically have world titles, e.g., FM, IM, or GM. 2200 is the USCF national master level, a level that is respectable world wide and considered by some to be the low end of the chess professional level. Of course, there are many chess masters that consider themselves amateurs.
I think scholastic player ratings often lag their ability because they improve quickly due to their interest, focus, vast amount of available time, energy, and in many cases support and resources from their parents. So, when they play in events with adults (that are often higher rated due to experience but are distracted by work, family, and less energy) they often gain points. I agree these rating point gains are often re-distributed later to others at scholastic events. But, as one improves they re-distribute less and keep more for themselves.
Of course, everyone is different but I would expect a 1000 player to have little in the way of endgame skill or experience. But, should be able to routinely mate with, e.g., K+R v. K or K+Q v. K. And, know the basics of how to Queen a Pawn, e.g., K+P v. K, and how to watch out for stalemates. They probably have never heard of the “wrong” Bishop in a K+B+Rook P v. K ending.
I would not expect a 1000 player to have good middlegame skills. They probably have heard about taking the 7th rank, and might have heard of good and bad Bishops. The might have heard of the Bishop pair being generally good but may not know when two Knights are better. But, they probably have never heard of an isolated queen pawn and how to handle such positions. They also probably think doubled pawns are always bad.
A 1000 player will probably have some opening knowledge of a couple openings, and probably know some of the axioms, e.g., Knights before Bishops, Castle early. Yet they often violate these guidelines. And, the opening knowledge is probably book memorization rather than an understanding of how to play the opening, and what squares are important and why. Or, which moves are thematic and why.
A 1000 player probably can see simpler tactics but games with 1000 players are often decided by blunders, e.g., a hung piece or a combination with one or two moves. So, buy and read 1001 Combinations by Reinfeld.
Some get sucked into the trap of spending too much time studying openings in the hopes of catching their opponent in a trap. Here, middlegame and endgame skills suffer. And, endgame skills are the most difficult to acquire and can take years. Some coaches recommend beginners start there.
If you want your rating to go up you should play as much as possible. Lots of Blitz online but as many serious games as possible. If you can handle losing, play one section higher than required. Meaning, if you are a 1300 player, don’t play in the U1400 section, play in the U1600 section. Don’t go for the Open section–a 1000 player that gets creamed by a Grandmaster has no fun and learns little. There needs to be some struggle, some back and forth. Look for games with others within about 300 points or so of yourself. Playing stronger opponents will improve your game. Of course you are likely to lose more, but you will improve faster. Some kids are ready to handle events with adults, some are not. Each person is different. For some younger kids, playing adults can be intimidating, even scary. Some smaller kids cry when they lose; these ones are probably not ready for the bigger or more serious events.
Go over all your games–especially your losses–with a friend or coach if available. I have seen scholastic players toss the game scores of their losses. If you are serious and can afford lessons, look for someone with a rating at least 400 points higher than you. A 2200+ player would be preferred but I know a “B” player that is an excellent scholastic coach. 1000 level players don’t need to seek out a Grandmaster for lessons but if you can afford it, a stronger coach can’t hurt. Also, lessons in person are much preferred but you can get them online too.