Execute stored procedure using variables entered and send output as parameter to save

What I am trying to do

I have a stored procedure in SQL Server that takes in a first and last name as parameters and outputs an ID. The goal is to execute this stored procedure and send it to my database on save.

What I have done

I have imported my stored procedure via the model browser and made a function import. I selected a collection of scalar string because i read this ("Scalars: it means stored procedure will return single value of selected type like binary, Boolean, byte etc. )

This is the code that I am working on right now but I do not think I am on the right even after making many variations.

public ActionResult Create([Bind(Include="id,firstname,lastname")] school_client school_client)
{
    using (var ctx = new invent_stuEntities())
    {
        var idParam = new SqlParameter {
                     ParameterName = "@firstname", school_client };

        var idParamB = new SqlParameter {
                     ParameterName = "@lastname", 
                     Value = school_client.lastname };

        //Get student id based on first and last name  
        var studentlist = ctx.Database.SqlQuery<Assign_studentid>("exec Assign_studentid @firstname,@lastname", idParam, idParamB).ToList<Assign_studentid>();

        if (ModelState.IsValid)
        {
            school_client.clientid = studentlist; // Send to database
            //  school_client.clientid = "TEST001";
            db.school_client.Add(school_client);
            db.SaveChanges();

            return RedirectToAction("Index");
        }
    };

    return View(housing_client);
}

The problem

I cannot get to pass the result of my stored procedure into my database like how I hardcoded it here

school_client.clientid = "TEST001";

Would like some assistance in editing my code so that my procedure can create run on insert.

Thanks