..map is not a function

Here, I fixed it for you. codesandbox.io/s/exciting-cdn-ip9w...
The issue was in the handleView method you were using the '!' on an array not a boolean.
Also, there was an issue in the mapping of teachers because React was missing the 'key' prop in order to render the teachers properly.

It was a small mistake @josephSam check what I changed here codesandbox.io/s/reverent-sun-oppw...

handleView = e => {
e.preventDefault();
let ta = this.state.showPersons;
this.setState({
showPersons: !ta
});
};