Your approach is not intuitive because you're presenting a score proportional to energy consumption but you score players according to the inverse of that. Calculate a score for participants which matches the intuitive mental model of an elementary school child (bigger/higher is better) and chart that value. In simple words...invert the score you use in your chart.
One UX golden rule is to design with the persona in mind.
What is perfectly clear for an educated adult may still be incomprehensible for an elementary school child.
Maartinus in his answer made a very good point: in games the word "score" carries the meaning of "higher is better" (with few exceptions like Golf and Ramino).
I am not an educator, gaming is an important part of children development but competition should be addressed carefully. Consider this answer a starting point to further investigate with the help of a professional educator.
I marked some points with †, I strongly recommend you discuss these suggestions with children's educators: they may be opinionated, they may need a psychological studies background to support them (which I do not have) or they may relate to children's culture and education level.
This answer is only half about UI design (how to present data), the most important part IMO is the overall eXperience to make this game pleasurable and educational while keeping in mind the intended audience.
Formulas, values and names are purely illustrative, knowing your domain I'm sure you can do much better than me.
Given this data:
Team 1: 34
Team 2: 22
Team 3: 56
Team 4: 16
We do not have an absolute reference value (if you had then simply reverting X axes might give you the desired result) then we have to normalize the energy efficiency field. I simply used
100 - Value / Maximum * 100.
Does it make sense? Let's take a quick look adding data bars:
To an increasing energy consumption (regardless how this is calculated) we have now an inverted normalised index to show the energy efficiency.
I'm using 100% as I best and 0% as worst. Some elementary school children may have more difficulties with bigger numbers or with decimals† (truncate them when presenting data.) If accuracy isn't your top priority then you may use [1..10] scale which should be even more intuitive†.
I do not know† if kBTU/ft2/yr is an appropriate unit of measure to use when targeting young children. That's why here I'm talking about "energy efficiency index", a pure number that everyone can understand.
How to present these information? If you wish to use bars now it should be easy:
Now teams performing better have intuitively a higher score. You may want to compare energy usage on the same chart. Because efficiency is the inverse of the usage and we are working with normalised data the whole is always 100%.
We have a team with a 0 score, it's not visually appealing but, more importantly, this value will never change and worst performing team will always have a score of 0. Competitors are children then we might want to provide some feedback of their progress† (or at least to show that something is happening). This may help morale and self-esteem†.
To solve this we may normalise using the sum instead of the maximum value:
If values are pretty high you may start X axes from a non-zero value. It has the positive effect to exaggerate differences and maybe stimulating a slightly competitive behaviour†:
Note that this is border-line with cheating with data, always include axes values: children should get used to good charts even when favouring visual appeal. It may be even a small discussion point (if they are old enough) to illustrate how poorly designed charts are misleading (and to quickly scan for signs of intentionally misleading ones†.)
I can't honestly understand from you chart what the X axes is. Time? Usage? Usage*time? Also, if you're working with a time axes IMO bars aren't the best choice. I'd calculate an index and plot it as line chart.
I didn't do it in these examples but you should order teams according to their score†. Another answer already addressed this. Your audience is made of children then feel free to add decorations and colors as appropriate† (without hiding data, of course).
Acrcturus, in his answer, suggests to add a marker for the winner. I think it's a good recommendation but I'd add special mentions for all the others† (even worst performing ones): constantly improving trend, best performing in last quarter, most stable index and so on. Ideally each team should have a mention for something.
There are many more things to say about this (especially in view of a retrospective† lesson) to help them to understand how the parts contributes to the whole (let's imagine one very efficient building in a world of highly inefficient ones). It's a stimulating topic but outside the scope of this question...