How can I get data outside the loop when using loop with $.get

you must use the callback function or something like this.

because the $.get is async function and when

console.log(school);

execute(!) the school is not evaluated yet.

you can use some things like this.

    a = ["{"sid":"13485"}","{"sid":"25114"}","{"sid":"45145"}"]

    for (var i = 0; i < a.length; i+=1){
       .$get('url' + "?params=" + a[i],function(data2){             
           school = data2['data']; 
           console.log(school);
        });
    }

or

a = ["{"sid":"13485"}","{"sid":"25114"}","{"sid":"45145"}"]
var  school ={};
for (var i = 0; i < a.length; i+=1){
   .$get('url' + "?params=" + a[i],function(data2){             
       school = data2['data']; 
       whenitready();
    });
}

function whenitready(){
   console.log(school);
}

If you need to wait until all your requests are done, you need something like this:

var endpoints = [];
for (var i = 0; i < a.length; i+=1) {
  endpoints.push($.get('url' + '?params=' + a[i]));
}
$.when.apply($, endpoints).done(function () {
  // Function arguments array differs if we have one or more than one endpoint.
  // When called with one endpoint arguments is an array of three elements [data, textStatus, jqXHR].
  // When called with more than one endpoint arguments is an array of arrays [[data, textStatus, jqXHR], ...].
  // Normalize the single endpoint to the generic list one.
  var args = endpoints.length > 1 ? arguments : [arguments];
  for (var i = 0; i < args.length; i++) {
    var data = args[i][0];
    // Do stuff here with every data received...
    school = ... 
  }

  console.log(school);
});