This:
What bugs me the most is the lack of colons or quotation marks or any other kind of punctuation...
Would you be able to give some context to what you are actually wanting to say.
Do you mean to say:
- "I know the difference between the demands of undergraduate and postgraduate study"
- "I know about the differences between levels of education as a subject of study" - i.e. in that you are applying for a course to study education
- "I know that the level of education across a range of different demographics varies significantly" i.e. you are aware of different abilities or educational expectations of a varied group
Regardless, the sentence should read thusly:
I have become aware of the difference(s)* between education levels.
*This depends upon whether you think there is just one difference between levels, or many differences.
I would strongly recommend that you reword it entirely dependant upon what you want to actually say.
Maybe it's 'have become' as that implies you were blissfully unaware of the differences of education for a large portion of your life.
I review postgraduate applications, showing that you have learned the difference between the expectations of different levels of study isn't a bad thing, though I would qualify it with some kind of example - 'I am aware... because I embarked grad level research in my dissertation' for example.
Personally, I would go into detail to say exactly what levels (and what differences) you are talking about - though this might be clear from the context.