This is a fairly easy tweak using jQuery:
function GridCreated(sender, eventArgs) {
// Set group header rows as clickable
$(".rgGroupHeader").each(function () {
$(this).find("input").click(function (event) {
// Prevent bubbling from initiating an infinite loop
event.stopPropagation();
});
$(this).click(function () {
// Pass the click on to the expand/collapse button
$(this).find("input").click();
});
});
}
Then just wire up the event in your RadGridmarkup:
<ClientSettings AllowGroupExpandCollapse="True">
<ClientEvents OnGridCreated="GridCreated" />
</ClientSettings>