Do you agree with the US Supreme Court's view that Congress does not have the legislative power to create gun-free school zones, and that this power is best left to regulation under state law? (See United States v. Lopez)

That is a very difficult question because of the complexity of states’ powers compared to the Supreme Court. I believe the Supreme Court has the power to do pretty much whatever it desires if it came to making that decision (although it would necessitate a court case on that subject being appealed all the way to the Supreme Court for it to occur). However, the most likely case scenario would not include the Supreme Court, so I will say that I agree that they wouldn’t take those steps.
The reasoning behind this is primarily centered on the fact that education is typically relegated to the states currently. Education budgets, curricula, and decisions are all currently held by each state, and so each state would have the opportunity to make its own decisions regarding gun-free zones. Eventually, if that step were taken, I believe it would spread nationwide, perhaps with the aid of the Supreme Court, but it would begin with individual states’ choices before being carried to those extremes.

To answer your question, you will have to decide whether the federal government's authority exceeds that of individual state governments in regards to gun laws. It certainly is a controversial issue. 
In United States v. Lopez, the United States Supreme Court ruled that Congress could not use the Commerce Clause to justify its prohibition of guns in school zones. The Supreme Court argued that gun violence was not a subset of interstate commerce. 
Those who argue that gun issues should be decided by individual states cite the Tenth Amendment as the basis of their claims:

The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people. 

To date, at least nine states have passed what are called nullification laws, which assert that individual states have the power to reject any federal law they consider unconstitutional. However, a federal judge ruled in early 2017 that Kansas cannot nullify federal gun laws. The judge likely based his decision on what is called the Supremacy Clause in the Constitution, which allows federal law to supersede state law.
So, this certainly is a very controversial issue. To answer your question, you will have to decide:
1) Whether the Supremacy Clause supersedes the Tenth Amendment.
2) Whether concealed-carry teachers and students are a danger or a help during a gun attack on a school. This is a very sensitive topic.
3) Whether Congress is right in arguing that prohibiting guns in a school zone is a federal prerogative under the Commerce Clause. The Commerce Clause allows the federal government to regulate commerce among the states and commerce between America and other nations.
https://www.oyez.org/cases/1994/93-1260