after_update.rb

class EnglishStudentsController < ApplicationController
  def update
    @english_student = User.find(params[:id])

    respond_to do |format|
      if @english_student.update_attributes(english_student_params)
        format.json { render json: { message: "Student updated successfuly" } }
      else
        format.json { render json: { message: "Student could not be updated" } }
      end
    end
  end
end

User < ActiveRecord::Base
  after_update :update_todays_english_attendace, if: self.level_changed?

  def update_todays_english_attendace
    english_attendance = english_attendances.find_by(
      date: some_date,
      temporary_level: false
    )
    english_attendance.level = level
  end
end