I need a website where I can enter phrases and determin my childs
educational writing level.  Example: much like asking you, only hit
submit and obtain immediate results.

They have all kinds of expensive tests for this.

Hitting submit for immediate results is not possible. A web
application like that would need artificial intelligence and thousands
of conditionals.

A phrase is given.
A full dictionary is used.
An artificial intelligence program is used to evaluate if the sentence
makes logical sense.
A spell check figures out what they might have been trying to say.
A comparison check would be made to determine which level the writing matches best.

Take the SATs. Ask a some teachers at your local at a public school
after showing them a sample essay.

The more you make them write the better they get. It might be better
to spend any money on a tutor rather than a test.

When people write a composition, they are using language to express
their ideas. Evaluating the education writing level is difficult
because a variety of factors (critical thinking skills, options in how
to present an idea, perception of audience, grammar, lexis
(vocabulary), etc.) all contribute to the 'level' of the final
product.

Having said that, however, there is a function within the WORD
software program which will tell you the readability level (at what
grade level) of a piece of writing. Readability generally refers to a
combination of the length of sentences used and the number of
syllables in the words used in the sentences. The more complicated the
idea, the longer it will take a writer to express it and the more
sophisticated will be the words s/he uses.  There are a number of
different readability formulae.

1. To access this function in WORD 2000 here's what you do:
open a file which a sample of the writing for which you want to check
the readability level

2.  On the STANDARD toolbar, open the TOOLS menu and click on OPTIONS
and then click on the SPELLING & GRAMMAR tab at the top. Under the
Grammar portion at the bottom of that page, select the SHOW
READABILITY STATS.  Close out the menu.

3. On the STANDARD toolbar click on the SPELLING/GRAMMAR check icon.
This will reveal the readability stats for that sample.

If you have any problems, click on HELP and type in READABILITY in the
Microsoft WORD help.

For reference, according to WORD, the readability level of the first
paragraph of my comment is 12th grade.