form_for undefined method `user_path'

you have a students_controller which corresponds to the resources :students line in your routes.rb. This creates routes that uses the word students like students_path and new_student_path. When using form_for(@record), the url is determined from the objects class. In this case, @record is a User so the path is users_path when the object is a new record and user_path(@record) when the object is persisted. since you don't have a users_controller defined, you need to manually set the url of the form_for to fix this error

form_for @user, url: student_path(@user), html: { method: :put } do |f|

now, if you're using a partial called _form.html.erb and uses this on both the new and edit actions, you're going to have a problem since the urls for both new and edit actions are different. you have to change your views to something like this

# new.html.erb
form_for @user, url: students_path, html: { method: :post } do |f|
  render 'form', f: f

# edit.html.erb
form_for @user, url: student_path(@user), html: { method: :put } do |f|
  render 'form', f: f

# _form.html.erb
f.text_field :name
f.text_field :title

If you are here because of the namespace (like me 10 minutes ago) you'll need this:

For namespaced routes, like admin_post_url:

<%= form_for([:admin, @post]) do |f| %>
 ...
<% end %>

from the doc

i fix it with local variables in render . In rails 5 - form_with tag:

# new.html.erb
  render partial: 'form', locals: {user: @user, url: students_path}

# edit.html.erb
  render partial: 'form', locals: {user: @user, url: student_path(@user)}

# _form.html.erb
form_with  model: user, url: url, local: true do |f|
  f.text_field :name
  f.text_field :title
end