Cities: Skylines II

The "Top of the Class" achievement requires you to build a city where at least 15% of the population has a university level of education.

Note that the description is missleading because you'll have to reach 15% of "Highly educated" citizen and you can monitor the education levels of your population in the city information panel.

Here are some tips to get it done quickly :

1. Build a city with access to all services.
2. Invest your development points in "education & research", build all research facilities of graduation and interest in university.
3. Provide education buildings for all your citizen, the capacity must be in the green. This will provide the opportunity for your citizens to pursue higher education..
4. Build all "office signature buildings", this tips is for advanced cities as they aree pretty hard to unlock but each will give you +1% university graduation chance and +5% interest in University Education (city-wide).
5. Increase Accessibility: Make sure the university is easily accessible to your citizens. This can be achieved by building efficient transportation networks such as buses, trams, or metros that connect residential areas to the university.
6. As your city grows, you may need to build more universities or expand existing ones to accommodate more students. Keep an eye on the capacity of your universities and increase it as needed.
7. Attract talent to your city and make the idiots go away : I think this is the best way to obtain the achievement in no time... Go to the Economy panel and in the "taxation" tab, you can develop the residential tax rate and max it for "uneducated and poorly educated, put it to 15 for ducated and 1% for well educated & highly educated. Low taxes encourage citizens to move in and higher taxes will drive them away.
8. You can monitor the education levels of your population in the city information panel. Here, you'll be able to see the percentage of your population that has a higly educated level.

Be patient, my achievement popped after 15 min in max speed at 15% of "highly educated" citizen.