No, we make no guarantees of this sort. Our application is a learning tool to help people learn about investing. Although we try to make portfolio values as accurate as possible, there are limits to this simulation.
The most obvious limitation is that real-life trades are part of "the market" and thus affect it. While an individual's effect on a large-cap stock that trades millions of shares a day is very minimal, the effect on a small, thinly-traded stock is much greater. In these cases, it's much more likely that a large trade would affect the price. We put artificial rules in place to minimize the discrepancies that arise, but these rules will never be perfect. We attempt to fill orders at a realistic price, but there is no guarantee that the same price would be received with a real trade. Other limitations include our use of delayed data, errors in programming, bad quotes from our data feed, the psychological difference between using real money and virtual money, etc.
The bottom line is that we hope you learn something out of the simulation but please realize that our game is simply a model and that no model is perfect.