This is the kind of thing I would prepare if asked to present project management to school students. And I would probably adopt a flipchart style. (This would save having to present a monotonous deck of slides.) I would do something really simple.
First the students would want to hear something about the kind of projects that are done and why they are important all over the world. Students like to hear about the exciting real world and there's nothing more 'real' than a good project! Then I'd explain that projects always bring something new, to the world or to an industry, and they need to be well managed, especially when they are complex and difficult (and they usually are).
Much can go right or wrong, and you can easily rub some people up the wrong way because you are usually replacing one set of things by something else. This means managing the stakeholders' expectations - including customers, but also project participants and team members, other people in the company, investors, the public, etc.
I would explain that projects are always about managing people and their reactions, that is the benefits, as well as the very important triple constraint. I would explain the triple constraint, by saying that delivering quality is about quantifying the expectations of the stakeholders and agreeing on the priorities. I would say that the project has to be organised so that we know what work has to be done to meet expectations and even to give people some nice surprises so that they will want to work with us again in the future.
And I'd say a few words about the work breakdown structure and how you need people to be responsible for all of the different parcels of work that are defined to make sure you meet the objectives. In the triple constraint I would say that sometimes the technical requirments are very well defined, the budget quite fixed and managing the project is mostly about managing time. I would give some examples - e.g. building a metro system or a new airport.
And I would mention the critical path method. I would say that sometimes the date is very fixed and the project content is quite well known, like with the Olympic Games. In these cases, the project is mostly about managing costs and resources: methods such as the critical chain, and performance management (measuring the value of work done) could be mentioned.
I would say that very often in modern business projects the budget is fixed and the time very tight as well, as in launching a new product ahead of the competition. With these projects scope needs to be managed carefully and the project designed so that the most important things are delivered in early versions, according to the critical purpose of the project, which has to be agreed and worked upon with the stakeholders.
I would select one of these projects and talk about it a bit more, making it look and sound and feel very interesting, explaining why it is important, and talking about what can go right and wrong, and why it is a challenge for the companies concerned. I would say a word about how the project manager's job depends upon their ability to operate in a complex organisational context, with the support of a sponsor and listening to the voices of customers and experts.
Then I would say that in general projects are fascinating, interesting, engaging and a good career choice because all over the world, in every industry and in every company and in every department of every company you have new things going on that need good managers.
You don't need to understand all of the technical details, but you have to be able to get people to work together and remember to ask the stupid questions that inspire people to think: like, "What will it have to do to be useful?", "What do I need in order to get started?" and "How will I know when I have succeeded? How can I measure that?" I'd say that it isn't usually very easy to manage a project, because all projects go through a storming phase when people don't agree, and everyone starts to think that everyone else on the project is an idiot. And the students will know this! But, I would explain that the work breakdown structure helps to define all the work leads the project through this stage.
As a conclusion, I would claim that project managers are the people who are needed to turn the problems and challenges of this world into solutions.