Another way to go about it is to use a model for the options, set default selection in the model and have your controller handle the logic of doing select all.
angular.module("app", []).controller("ctrl", function($scope){
$scope.options = [
{value:'Option1', selected:true},
{value:'Option2', selected:false}
];
$scope.toggleAll = function() {
var toggleStatus = !$scope.isAllSelected;
angular.forEach($scope.options, function(itm){ itm.selected = toggleStatus; });
}
$scope.optionToggled = function(){
$scope.isAllSelected = $scope.options.every(function(itm){ return itm.selected; })
}
});
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"> </script>
<div ng-app="app" ng-controller="ctrl">
<form id="selectionForm">
<input type="checkbox" ng-click="toggleAll()" ng-model="isAllSelected">Select all
<br>
<div ng-repeat = "option in options">
<input type="checkbox" ng-model="option.selected" ng-change="optionToggled()">{{option.value}}
</div>
</form>
{{options}}
</div>