Kendo grid json post

I have an MVC application using a Kendo grid as follows:

var products = [{
        ProductID: 1,
        FullName: "Chai",
        IsHeadmaster: "T"
    }];

$("#teachers").kendoGrid({
    dataSource: {
        type: "json",
        transport: {
            read: function (e) {
                // on success
                e.success(products);
                // on failure
                //e.error("XHR response", "status code", "error message");
            },
            update: {
            type: "POST",
            url: "/Home/UpdateTeachers",
            dataType: "json",
            contentType: "application/json"
                        },
            parameterMap: function(data, operation) {
                if (operation === "update" || operation === "create") {
                    return JSON.stringify({product: data});
                }
                return data;
            }

        },
        batch: true,
        schema: {
            model: {
                id: "TeacherId",
                fields: {
                    TeacherId: { type: "number" },
                    FullName: { type: "string" },
                    IsHeadmaster: { type: "boolean" }
                }
            }
        }
    },
    toolbar: ["create", "save"],
    columns: [
        { field: "FullName", title: "Teacher" },
        { field: "IsHeadmaster", title: "Is a Headmaster?", width: "120px" },
        { command: ["destroy"], title: " ", width: "85px" }],
    editable: true
});

And my controller as:

public JsonResult UpdateTeachers(string models)
{
 // do update here
}

The grid loads and displays perfectly, however when i try to make an edit and update i get the following error:

Unhandled exception at line 6684, column 17 in http://localhost:5227/kendo/js/kendo.web.js

0x800a01b6 - JavaScript runtime error: Object doesn't support property or method 'call'

I'm using JQuery 1.8.2.

Any ideas/help would be greatly appreciated?

You may try this by editing below code

instead of

return JSON.stringify({product: data});

use

return { models: kendo.stringify(data.models) };