SOLSC What good is the data?

It is Tuesday and this is a "Slice of Life" for Two Writing Teachers.  Check out their website for lots more reflections on teaching.

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She is full of energy, and endless motion.
She visits every center, every day, several visits to each one,
never staying very long.
She loves the sensory table.
She is always busy, up to something.
I have to keep my peripheral vision on her,
if not my full attention.
Yes, she is a "dumper" -
if I'm not right there next to her,
she will dump the beads all over the table,
empty the blocks onto the carpet,
fill a purse with all the pretend food and
dump it out elsewhere in the room.
She is happy and non-stop.

I wasn't surprised by the alphabet assessment.
She didn't recognize any of the letters.
She's just not ready to see these yet, I rationalized.
This is a mover and a shaker.
Her pre-literacy will be song, dance, books, and stories...
we'll get to letter recognition much later...
if not this preschool year, then perhaps pre-k.

At least this is what I was thinking until yesterday.

She was frenetic at the end of the day,
trying to get into the closed sensory table,
reaching for scissors to cut paper into small bits,
opening up the paints at the easel, long after they had been closed for the day.
I didn't want to say "no" anymore.
I scooped her up into my arms, saying,
"I need a minute with you - I need a hug!"
This freed me from having to follow her around,
while dismissing children to their families.
This kept her from getting into any more mischief.

While perched there,
head at my head level,
she surprised me.
She began reading a sign I had posted for adults...
putting her finger at each letter and reading aloud,
accurately,
each letter,
one by one.

What?

My data says,
consistently says,
she does not know any letters.

Yet, here she is,
focused,
reading every letter accurately.

Aieeeee.

What does this tell me about my assessment?
What have I learned about her?
How will I help her to focus from now on?
What else have I missed about her?
What have I assumed?
What good is the data?